8queen solver

queen.hs

dat' n =replicate n [0..(n-1)]

qvalid=all (\v -> case v of
               [] -> False
               _  -> True)

qdrop:: Int->[[Int]]->[[Int]]
qdrop pos board=
  let b=zip [1..] board
      f d p=not (abs (pos-p)==d || pos==p  )
    in  map (\(d,p) -> filter (f d) p) b

queen []=[]
queen [x]=[x]
queen (x:xs)=
  let b'  = map (\v -> (v,qdrop v xs)) x
      b'' = filter (\(_,y) -> qvalid y) b'
      m   = map (\(v,b) -> map (\c->v:c) (queen b))  b''
  in foldl (++) [] m

main=do
  print $ length $ queen $ dat' 1
  print $ length $ queen $ dat' 2
  print $ length $ queen $ dat' 3
  print $ length $ queen $ dat' 4
  print $ length $ queen $ dat' 5
  print $ length $ queen $ dat' 6
  print $ length $ queen $ dat' 7
  print $ length $ queen $ dat' 8
  print $ length $ queen $ dat' 9
  print $ length $ queen $ dat' 10
  print $ length $ queen $ dat' 11
  print $ length $ queen $ dat' 12